Description du sujet de thèse

When a hot surface is brought into contact with a liquid, if the temperature is high enough, a Leidenfrost state can be reached. In this case, a thin film of vapor is intercalated between the liquid and the substrate, insulating the liquid physically, mechanically, and thermally, thus preventing the boiling and cooling of the solid. This effect is observed in many industrial sectors, such as energy production, metallurgy, or aeronautics. It is the main subject of the European DTN Leidenforce project. We are studying this effect in a particular situation, with a cylindrical micrometer wire heated in a liquid bath at room temperature. When the thermal power supplied to the wire is sufficiently high, the Leidenfrost transition occurs, manifesting itself by a sharp increase in the wire's temperature. The objective of the thesis is first to characterize this transition in this complex geometry. A potential difference will then be applied between the wire and the liquid. Thanks to the small bending radius of the wire, peak effects are induced, significantly increasing the thermal and electric field within the Leidenfrost film. We will study how this electric field modifies the properties of the films (thickness, stability) and whether specific reactions can be induced (plasma, chemical reactions, etc.). Secondary project: During a specific metallurgical treatment, a device is placed in a bath, heated above the Leidenfrost temperature, and subjected to a high voltage. This high voltage generates a plasma and chemical reactions in the vapor layer. Maintaining the Leidenfrost state under these conditions presents challenges. The thesis will identify the relevant parameters involved.

Contexte de travail

The student will be enrolled in a PhD program at Lyon 1 University, including mandatory scientific and cross-disciplinary courses. He/she will be integrated into the L&I and PNEC teams of the Institut Lumière Matière, a physics institute of Lyon 1 University, in France, which has more than 300 collaborators including around a hundred doctoral students and post-doctoral fellows. The continuum between fundamental research, responding to major societal challenges and innovation is at the heart of this unit's approach. All staff are committed to promoting excellence and ethical and responsible research. Its scientists explore six major thematic fields: Materials, energy, photonics, Soft matter, Nanosciences, Optics and ultrafast dynamics, Theory and modeling, Living, health, environment. As a doctoral student of the DTN project, he/she will have to participate in the life of the two iLM research teams as well as regularly in meetings, training courses and doctoral schools organized within the European consortium (2 to 3 times per year). A 3-month stay at the Metallurgical Research Center in Liège (Belgium) is planned in the second year.

Contraintes et risques

Experimentl work with thermal effect and high voltage